Android，试图找到逻辑来存储纬度和经度值从用户的位置

Question

如问题所述，我希望将经度和纬度保存为双精度，以便在程序中使用它们。

我可以使用setOnMyLocationChange侦听器，并从那里从UserLocation类创建一个对象，我已经创建了存储时间和长度。

我可以使用UserLocation.getLat()在侦听器方法中打印它，但我不能存储变量以便在程序的其他地方使用它。我会把我认为相关的代码贴出来。

我将UserLocation l存储为全局变量

UserLocation l;

这里我得到一个null对象引用l.g getlat()，即使我可以引用侦听器中的变量。

else if (city.equals("myLocation")) {
            map.setMyLocationEnabled(true);
            Location myLocation = map.getMyLocation();
            map.setOnMyLocationChangeListener(this);
//            map.setOnMyLocationChangeListener(null);
            lat = l.getLat();
            lon = l.getLng();
            Toast.makeText(this, lat+" is latMy in map activity ", Toast.LENGTH_LONG).show();

        }

这里我可以打印出值

  @Override
    public void onMyLocationChange(Location location) {
        latMy = location.getLatitude();
         lngMy = location.getLongitude();
        l = new UserLocation();
        l.setLat(latMy);
        l.setLng(lngMy);
        Toast.makeText(this, latMy+" is latMy in LOCATION CHANGE ", Toast.LENGTH_LONG).show();
    }

这是我的UserLocation类

package com.example.its.citymap;
public class UserLocation {
    private double lat; 
    private double lng; 
    public double getLat() {
        return lat;
    }
    public void setLat(double lat) {
        this.lat = lat;
    }
    public double getLng() {
        return lng;
    }
    public void setLng(double lng) {
        this.lng = lng;
    }
}

我已经搜索并尝试了很多，但无法找到一个可靠的答案。

谢谢

Answer 1

首先检查启用了哪些提供程序。有些可能在设备上被禁用，有些可能在应用程序清单中被禁用。

如果有可用的提供程序，我启动位置侦听器和超时计时器。在我的例子中是20秒，对于GPS来说可能不够，所以你可以放大它。

如果我从位置侦听器获得更新，我使用提供的值。我停止监听器和定时器。

如果我没有得到任何更新和计时器失效，我必须使用最后已知的值。

我从可用的提供程序中获取最后已知的值，并选择其中最近的值。

下面是我如何使用我的类:

LocationResult locationResult = new LocationResult(){
    @Override
    public void gotLocation(Location location){
        //Got the location!
    }
};
MyLocation myLocation = new MyLocation();
myLocation.getLocation(this, locationResult);
And here's MyLocation class:
import java.util.Timer;
import java.util.TimerTask;
import android.content.Context;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
public class MyLocation {
    Timer timer1;
    LocationManager lm;
    LocationResult locationResult;
    boolean gps_enabled=false;
    boolean network_enabled=false;
    public boolean getLocation(Context context, LocationResult result)
    {
        //I use LocationResult callback class to pass location value from MyLocation to user code.
        locationResult=result;
        if(lm==null)
            lm = (LocationManager) context.getSystemService(Context.LOCATION_SERVICE);
        //exceptions will be thrown if provider is not permitted.
        try{gps_enabled=lm.isProviderEnabled(LocationManager.GPS_PROVIDER);}catch(Exception ex){}
        try{network_enabled=lm.isProviderEnabled(LocationManager.NETWORK_PROVIDER);}catch(Exception ex){}
        //don't start listeners if no provider is enabled
        if(!gps_enabled && !network_enabled)
            return false;
        if(gps_enabled)
            lm.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0, locationListenerGps);
        if(network_enabled)
            lm.requestLocationUpdates(LocationManager.NETWORK_PROVIDER, 0, 0, locationListenerNetwork);
        timer1=new Timer();
        timer1.schedule(new GetLastLocation(), 20000);
        return true;
    }
    LocationListener locationListenerGps = new LocationListener() {
        public void onLocationChanged(Location location) {
            timer1.cancel();
            locationResult.gotLocation(location);
            lm.removeUpdates(this);
            lm.removeUpdates(locationListenerNetwork);
        }
        public void onProviderDisabled(String provider) {}
        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    };
    LocationListener locationListenerNetwork = new LocationListener() {
        public void onLocationChanged(Location location) {
            timer1.cancel();
            locationResult.gotLocation(location);
            lm.removeUpdates(this);
            lm.removeUpdates(locationListenerGps);
        }
        public void onProviderDisabled(String provider) {}
        public void onProviderEnabled(String provider) {}
        public void onStatusChanged(String provider, int status, Bundle extras) {}
    };
    class GetLastLocation extends TimerTask {
        @Override
        public void run() {
             lm.removeUpdates(locationListenerGps);
             lm.removeUpdates(locationListenerNetwork);
             Location net_loc=null, gps_loc=null;
             if(gps_enabled)
                 gps_loc=lm.getLastKnownLocation(LocationManager.GPS_PROVIDER);
             if(network_enabled)
                 net_loc=lm.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
             //if there are both values use the latest one
             if(gps_loc!=null && net_loc!=null){
                 if(gps_loc.getTime()>net_loc.getTime())
                     locationResult.gotLocation(gps_loc);
                 else
                     locationResult.gotLocation(net_loc);
                 return;
             }
             if(gps_loc!=null){
                 locationResult.gotLocation(gps_loc);
                 return;
             }
             if(net_loc!=null){
                 locationResult.gotLocation(net_loc);
                 return;
             }
             locationResult.gotLocation(null);
        }
    }
    public static abstract class LocationResult{
        public abstract void gotLocation(Location location);
    }
}